Polycarbonates are used in various fields such as housing materials of appliances and office automation appliances because of excellent mechanical properties such as impact strength.
However, polycarbonates have drawbacks such as low fluidity and poor processability.
To improve the fluidity, the molecular weight of the polycarbonates themselves may be decreased. However, when the molecular weight of a polycarbonate is decreased, the impact strength is lowered. In general, a styrene-butadiene-acrylonitrile copolymer is mixed to improve the fluidity, however, a large amount of the copolymer must be mixed to obtain effective fluidity and as a result, the impact strength is lowered.
For the purpose of improving the balance between the fluidity and the impact strength of polycarbonates, an experiment of adding various vinyl polymers was carried out. This experiment is roughly divided into a trial of improving the fluidity of high-molecular weight polycarbonates having high impact strength and low fluidity and a trial of improving the impact strength of low-molecular weight polycarbonates having high fluidity and low impact strength.
For example, Japanese Unexamined Patent Application, First Publication No. Sho 56-143239, Japanese Unexamined Patent Application, First Publication No. Hei 1-65461, and Japanese Unexamined Patent Application, First Publication No. Hei 1-268761 describe that the impact strength of polycarbonates is improved by adding a polymer containing an alkyl acrylate rubber.
However, the resin composition thus obtained has insufficient fluidity and insufficient impact strength.
Also Japanese Unexamined Patent Application, First Publication No. Sho 62-138514 describes that the fluidity of polycarbonates is improved by adding a polymer comprising an aromatic vinyl monomer and methyl methacrylate.
However, the resin composition thus obtained has low impact strength.
Japanese Unexamined Patent Application, First Publication No. Hei 5-140435 describes that the fluidity of polycarbonates is improved by adding a low molecular weight polymer comprising an aromatic vinyl monomer and all alkyl acrylate.
However, since this low-molecular weight polymer contains a large amount of soft components, the polymer is sticky and has poor handling properties, such that blocking is likely to occur. Moreover, when test pieces have a large thickness, the impact strength is lowered.
Japanese Unexamined Patent Application, First Publication No. Hei 1-268761 describes that the addition of a high-molecular weight alkyl methacrylate polymer is effective to prevent sagging of polycarbonates during extrusion molding.
However, the addition is not effective to improve the fluidity.
Japanese Unexamined Patent Application, First Publication No. Hei 11-181197 describes that polycarbonates are superior in fluidity, heat resistance, transparency, and odors/fumes when a low-molecular weight aromatic vinyl polymer having a solubility parameter of more than 9.3 and less than 11.5 is added.
However, the resin composition thus obtained has low impact resistance.
As described above, although an experiment of adding various vinyl polymers has been carried out in the prior art, no experiment has ever succeeded in improving the balance between the fluidity and the impact strength of polycarbonates.